The present invention generally relates to gas turbine engine systems and, more particularly, to turbine scroll assemblies.
Turbine scroll assemblies have been used extensively in gas turbine engines. The turbine scroll assembly may be positioned within a combustor housing and may surround a radial nozzle. The turbine scroll assembly may comprise a turbine scroll with a spiral contour and gradual area reduction with one end open for gas inlet and a B-width that covers the entire circumference for gas to exit. The B-width may be the opening through which gas may pass from the turbine scroll to the radial nozzle during engine operation. Thin sheet metal with a high temperature capability may be used to fabricate a turbine scroll through a forming process. It also can be fabricated from thin wall casting processes. Machined rings may be welded to the sheet metal to form specified interface characteristics and structural reinforcement. Retention assemblies may maintain the position of the turbine scroll. The retention methods may include end support of the turbine scroll, suspension of the turbine scroll by axial fasteners, suspension of the turbine scroll by a suspension pin, or retention of the turbine scroll by clamps.
During engine operation, gas may pass through the B-width and enter the radial nozzle. Conventional turbine scroll assemblies may be useful for some low cycle and low performance engines. For more advanced systems used on high performance vehicles, such as aircraft, the turbine scroll assembly must meet additional requirements. Current needs for turbine scroll systems include the ability to control small amounts of gas leakage between components at various operating conditions for performance optimization. Two main operating conditions are an open-loop condition (e.g., ground maintenance or in-flight emergency power) in which the engine runs on its own power and a closed-loop condition (e.g., taxi condition and general flight conditions) in which the engine runs on the bleed gas of the main engine. For some high performance engines, the B-width of the turbine scroll assembly may not remain constant during various engine operations such as surging or transient due to excessive pressure or differential thermal growth and inadequate scroll retention methods. This, in turn, may reduce engine performance. Additionally, in some engine systems, gas may leak at the interface between the turbine scroll and the radial nozzle, which may also reduce engine performance. Retention systems and sealing assemblies have been disclosed.
Retention systems have been described in U.S. Pat. No. 6,443,699. These systems utilize a split ring inserted in an annular groove in a counterbore to accommodate a “snap ring” configuration. The ring is positioned adjacent the aft end face of a bushing to retain the bushing against axial movement. Although, the disclosed systems may provide improved retention methods, they may not be suitable for some applications because the disclosed split ring is not symmetric. For axially loaded applications, the split ring may lead to non-uniform loading in a circumferential direction. The non-uniform loading may allow misalignment of the turbine scroll causing engine performance loss and gas leakage.
A retaining ring system has been has been disclosed in U.S. Pat. No. 4,425,078. The described ring may be axially flexible and radially stiff. Unfortunately, for some applications a retention system having radial compliance is needed. Additionally, the described ring system may not be suitable for applications having axial loading. The axially flexible ring may allow gas leakage in some applications.
A sealing assembly has been described in U.S. patent application Ser. No. 2003/0122322. The describe assembly utilizes O-rings to seal between adjacent surfaces. Although, the described sealing assembly may reduce leakage in some applications, it may not be useful in some high temperature environments. Additionally, the described sealing assembly does not provide the radial compliance and the axial load desired in some engine applications.
As can be seen, there is a need for improved turbine scroll retention assemblies. Additionally, turbine scroll assemblies are needed wherein axially loading is uniform at a variety of operating conditions. Turbine scroll retention systems having radial compliance are needed. Further, assemblies are needed wherein the B-width remains constant during engine operation.